There are various methods for modifying the surface state of a substrate through a treatment using an appropriate agent to specifically improve certain surface properties. For example, in the field of mechanics, and in particular in the field of horology, but also in the field of jewellery, a surface of a piece or an element is often epilamized with an epilame agent to control and reduce the surface energy of said surface during use. More specifically, the purpose of an epilame agent is to prevent the spreading of oils or lubricants on the elements of a timepiece or piece of jewellery by forming a hydrophobic and lipophobic surface allowing the lubricant to remain in a predetermined place on the treated surface.
The standard epilame coating method is a dip coating process. It consists in dipping the timepiece in an epilame-coating bath, i.e. a solution of epilame agent in a solvent in a given concentration. The epilame effect depends on the concentration of epilame agent. In industry, the same epilame-coating bath is used for the epilame coating of timepieces for several months. Gradually as it is used, the quantity of epilame agent in the bath decreases (part of the epilame agent remains adsorbed/clings to the timepieces and the quantity of solvent in the epilame agent solution also decreases via evaporation. Thus, during use, the concentration of epilame agent in the epilame-coating bath changes. To limit these fluctuations, in industry, a concentrated solution of the epilame agent and/or solvent is regularly added to the epilame-coating bath. However, these additions are made in a very empirical manner, given that the current epilame-coating process does not allow precise information to be obtained as to the concentration of epilame agent. This results in epilame effects that vary significantly from one batch to another.